Illumination devices employing a laser light source are becoming prevalent since the laser light source is long-life compared to high-pressure mercury lamps and the like, the optical system can be downsized, and the electric power consumption is lower. Especially, by combining a laser light source with a light diffusion element such as a hologram, it is possible to illuminate a particular region with light having directivity and a breadth.
For example, Patent Document 1 discloses an illumination device that illuminates an illumination object region with a coherent light such as a laser beam diffused by a hologram record medium. Patent Document 2 discloses a display device including a transmissive hologram having a plurality of regions to which reconstructed images different from each other are respectively assigned and being capable of making a laser beam be incident on each region of the transmissive hologram and thereby projecting the assigned hologram reconstructed image onto a road surface.